Residue removers for electrohydrodynamic cleaning of semiconductors

ABSTRACT

The present invention relates to a method of modifying a surface. The method may include introducing a liquid to a first cluster generation site. The liquid includes an oxidizing agent, such as hydroxylamine. The liquid is subjected to electrical forces higher than a surface tension of said liquid to prepare a first plurality of clusters. Clusters of the first plurality of clusters are impacted upon the surface.

[0001] The application claims priority to Provisional App. No.60/455,439 filed Mar. 18, 2003, the disclosure of which is incorporatedby reference.

FIELD OF THE INVENTION

[0002] The present invention relates in general to a method andapparatus for cleaning surfaces of substrates, and in particular to theremoval of organic films, particulate matter and other contaminants fromthe surface of semiconductor wafers, by impacting the surface withdroplets comprising an oxidizer. In another aspect the invention relatesto a method of modifying said substrate surface by depositing amodifying agent, for example an organometallic agent capable of reactingto leave a metal atom, by impacting the surface with droplets comprisingorganometallic compounds.

BACKGROUND OF THE INVENTION

[0003] The removal of contaminants from surfaces is critical for theprofitable manufacturing and subsequent performance of many devices andprocesses. For example, device yields in semiconductor fabricationfacilities are adversely affected by defects caused by particulatesadhering to wafer surfaces. More than 80% of the yield loss of volume-manufactured VLSI's is attributed to particulate microcontamination. Asdevice geometries continue to shrink and wafer sizes increase, particlecontamination will have an ever increasing impact on device yields. Newtechnologies will be required to clean wafer surfaces to meet nationalgoals for producing 0.07 micron feature sizes by the year 2010. Therequirements for finer polishing are leading to smaller abrasiveparticles. It is now recognized that the future need in semiconductorwafer processing requires removal of particulates 0.1 micron in size andsmaller which are highly resistant to removal by conventional cleaningtechnologies. Present particle removal technologies become increasinglyineffective as “killer” particle size decreases.

[0004] Particles generated within process tool equipment, especially inthe backend of a multilevel process, represent a major source of yieldloss in terms of defective chips. At the present time, there is nocommercially available, in-situ cleaning instrumentation for processingwafers in vacuum. The requirements placed on surface cleanliness formicroelectronics device fabrication also apply to the manufacturing ofmicromachines and microsensors based on silicon or gallium arsenidewafer preparation technology.

[0005] In addition to cleaning semiconductor wafers and processingtools, the present invention also relates to the cleaning of ground orspacecraft optics such as mirrors, lenses and windows. Other areas ofapplication of the invention include the cleaning of silicon or othersubstrate materials to lower costs and uphold reliability during themanufacturing of flat panel displays; cleaning spacecraft thermalcontrol surfaces and solar panels; cleaning surfaces in preparedness fordeposition of thick or thin film materials to improve adhesion or growthdynamics; precision cleaning and removal of contaminants from vacuumchamber walls and internal mechanical/optical systems in majorfacilities such as the National Ignition Facility for fusion researchand surfaces critical for the control of pharmacologicalcross-contamination.

[0006] Additional areas of application for the present invention includethe cleaning of critical surfaces relevant to computers such as magneticdisk storage media. The continued evolution of computer technology hasresulted in increasing demands for chemically clean and particulate-freesurfaces. As computer technology continues to rely on microelectronicsdevices that shrink in size, product yield has become increasinglyvulnerable to chemical and particulate contaminants.

[0007] Thin film structures are used in a variety of industrialapplications including optical components, industrial platings, solarcells, wear and corrosion resistant coatings and coatings fortransmissive and reflective elements to name a few. Thin filmsstructures are adversely affected by the presence of chemical andmicron-sized contaminants which impede the growth, adhesion, wearresistance and stability of the films. The present invention provides anenhanced cleaning process for a variety of solid surfaces compared toconventional cleaning techniques used in the above applications. For areview of cleaning techniques for removing particulates from surfaces,see J. Bardina, “Methods For Surface Particle Removal: A ComparativeStudy”, Particulate Sci.Technol., 6, 121, 1988.

[0008] At present there are two principal methods of cleaning wafersurfaces: liquid phase or “wet” cleaning and gas phase or “dry” cleaningdesigned to remove process chemicals, films and particulatecontamination. These methodologies suffer from several drawbacks, themost serious being that no single technology rids surfaces of organicfilms, trace metallic elements or particulates simultaneously. In somecases, the cleaning process is a source of contaminants itself. Evenmegasonic techniques, which can remove particulates in a given sizerange may not be effective for removing particulates of about 0.1 micronor less. Furthermore, ultrasonic cleaning efficiencies show somedependency on particulate composition and morphology. Wet cleaningtechnologies also suffer by consuming large quantities of water. Theneed to conserve water and reduce costs associated with water usage areobvious. Additionally, wet cleaning technologies consume largequantities of environmentally hazardous chemicals such as inorganicacids, bases and etches including sulfuric acid, phosphoric acid,hydrofluoric and hydrochloric acids; ammonium fluoride; ammonium, sodiumand potassium hydroxides and hydrogen peroxide to mention a few. Thesematerials create proper handling and waste storage problems. The currentstatus of wet chemistry cleaning technologies is discussed by Hattori,“Trends in Wafer Cleaning Technology”, Solid State Technol. Suppl.,p.S7, May, 1995.

[0009] The use of dry ice snow flakes, formed by the expansion of liquidCO₂ jet sprays, have also been used to clean spacecraft optical surfacesand semiconductor devices. These applications are discussed in M. M.Hills, “Carbon Dioxide Jet Spray Cleaning of Molecular Contaminants”,J.Vac.Sci.Technol. A13(1), 30, January/February 1995 and R. Sherman etal. , “Dry Surface Cleaning Using CO₂ Snow”, J.Vac.Sci. Technol.,B9(4),1970, July/August 1991. Although capable of removing organic films andparticulates, CO₂jet sprays are ineffectual for removing submicronparticulates (<0.1 micron) to levels specified for futuremicrocontamination-free manufacturing of wafers.

[0010] Other “dry” cleaning technologies for removing contaminants fromsemiconductor wafers include gas-phase cleaning which uses reactivegaseous radicals formed by the excitation of process gases. Theseprocesses suffer from the use of complex chemistries which can result indamaged surfaces or removal of substrate material when attempting toremove particulate contaminants.

[0011] U.S. Pat. Nos. 4,896,035 and 4,835,383 disclose an ion detectionsystem and method for detection of low or high mass ions. U.S. Pat. No.4,762,975 discloses a method for producing ultrafine particles. U.S.Pat. No. 4,462,806 discloses a method for purifying metals andsemiconductors. U.S. Pat. No. 4,318,028 discloses production of an ionbeam. U.S. Pat. No. 4,264,641 discloses electrohydrodynamic productionof particulates. U.S. Pat. No. 4,124,801 discloses a method forseparating materials, such as isotopes. U.S. Pat. Nos. 3,893,131 and3,848,258 disclose an ink drop printer. The foregoing patents areincorporated herein by reference in their entireties.

SUMMARY OF THE INVENTION

[0012] One aspect of the present invention relates to a method ofcleaning or modifying a surface. In one embodiment, the method includes(a) introducing a first liquid to a first cluster generation site, thefirst liquid comprising an oxidizing agent; (b) subjecting the firstliquid to electrical forces higher than a surface tension of the firstliquid to prepare a first plurality of clusters, wherein the clustersare formed from the first liquid; and (c) impacting clusters of thefirst plurality of clusters upon a first portion of the surface. In step(c), the phrase “clusters of the first plurality of clusters” means atleast a portion of the first plurality of clusters. Advantageously, theclusters are less than a micron in diameter.

[0013] The oxidizing agent may comprise a hydroxylamine compound, e.g.,at least one of hydroxylamine, an (organic) derivative of hydroxylamine,a salt of hydroxylamine, and a salt of a derivative of hydroxylamine. Ina preferred embodiment, the first liquid comprises at least one solvent,such as water and/or a poly-alcohol, and at least one of hydroxylamine,a derivative of hydroxylamine, a salt of hydroxylamine, and a salt of aderivative of hydroxylamine. Preferred hydroxylamine compounds arehydroxylamine, an N-substituted hydroxylamine (N—H,R,OH)or anN,N-substituted hydroxylamine (N—R,R,OH) wherein the R is a C₁ to C₄alkyl, a carboxyl, or combination thereof.

[0014] Relative to the weight of the first liquid, the total weight ofthe at least one of hydroxylamine, a derivative of hydroxylamine, a saltof hydroxylamine, and a salt of a derivative of hydroxylamine is atleast 25 percent. For example, the total weight of the hydroxylamine, aderivative of hydroxylamine, a salt of hydroxylamine, and a salt of aderivative of hydroxylamine may be at least 0.25 grams, at least 0.30grams, or at least 0.35 grams per gram of the first liquid. The bulk ofthe liquid may consist essentially of at least one solvent.Alternatively, the bulk of the liquid may comprise at least one solventand other compounds, such as at least one of at least one corrosioninhibitor, at least one chelating agent, and optionally at least onemetallic compound. In a preferred embodiment, the oxidizing agentcomprises at least one of hydroxylamine and a derivative ofhydroxylamine and the total weight thereof is at least 25 percentrelative to the weight of the liquid. For example, the total weight ofthe at least one of hydroxylamine and a derivative of hydroxylamine maybe at least 0.25 grams, at least 0.30 grams, or at least 0.35 grams pergram of the first liquid. The bulk of the liquid may consist essentiallyof at least one solvent. Alternatively, the bulk of the liquid maycomprise at least one solvent and other compounds, such as at least oneof at least one corrosion inhibitor, at least one chelating agent, andat least one metallic compound.

[0015] In one embodiment, the first liquid consists essentially of atleast one hydroxylamine compound, and optionally but preferably, anamount of solvent sufficient to form a stable composition. As is knownin the art, some forms of hydroxylamine must be aqueous or dissolved ina polar solvent. For example, pure hydroxylamine is unstable unlessdiluted with at least about 50% water (or less preferably with othersolvents). Salts of hydroxylamine can be more concentrated or even beobtained and used in pure form, as can many organic hydroxylaminederivatives. In a preferred embodiment, the hydroxylamine is dissolvedin sufficient solvent, e.g., water, preferably very high purity water,so that the composition is stable. One embodiment of the first liquidconsists essentially of aqueous hydroxylamine. One preferred embodimentof the first liquid consists essentially of aqueous hydroxylamine, wherethe concentration of hydroxylamine is between 5% and 50% by weight.

[0016] In another embodiment, the first liquid may consist essentiallyof a hydroxylamine compound and a solvent. The solvent preferablycomprises at least two of water, an alkanolamine, an amide, a glycol, ordimethylsulfoxide. One preferred group is monoalkanolamines. The solventmay comprise an organic compound having at least one hydroxyl group. Forexample, the solvent may comprise an organic compound having fewer than20 carbon atoms and at least two hydroxyl groups.

[0017] In another embodiment, the first liquid having a hydroxylaminecompound and a solvent may additionally comprise an acid. The acid maycomprise, for example, at least one of nitric acid, acetic acid,sulfuric acid, peroxymonosulfuric acid, perchloric acid, peracetic acid,perchromic acid, periodic acid, perchloric acid, perbromic acid,perfluoric acid, and perboric acid. Preferred inorganic acids are nitricacid and phosphoric acid. Preferred organic acids include acetic acid,glycolic acid, maleic acid, malonic acid, oxalic acid, and gallic acid.Ascorbic acid or citric acid can be added Generally, the mineral acid ispresent in an amount between 0.1% and 5% by weight. The organic acid, ifpresent, can be added in an amount between 0.5% and 10%, for example.

[0018] In another embodiment, the first liquid comprises in addition tothe hydroxylamine compound at least one corrosion inhibitor. Thecorrosion inhibitor may comprise, for example, at least one ofbenzotriazole and a derivative of benzotriazole. Alternatively, thecorrosion inhibitor may comprise a dihydroxybenzene or atrihydroxybenzene, optionally substituted with one C₁ to C₄ alkylmoiety. As little as 1% can be useful. The total weight of the at leastone corrosion inhibitor may be at least 5 percent, at least 15 percent,or at least 25 percent, relative to the weight of the first liquid. Forexample, the total weight of the at least one corrosion inhibitor may beat least 0.05 grams, at least 0.15 grams, or at least 0.25 grams pergram of the first liquid.

[0019] Preferred first liquids comprise a hydroxylamine, water, and analkanolamine or aminoethoxyethanolamine.

[0020] In another embodiment, the first liquid may comprise periodicacid in an amount between 0.2% and 5%. Such a composition is preferablysubstantially free of hydroxyamine

[0021] In an alternative embodiment, the oxidizing agent may behydroxylarnine-free and comprise at least one oxidizing agent having atleast one peroxy group. For example, the oxidizing agent having at leastone peroxy group may comprise at least one of hydrogen peroxide, ureahydrogen peroxide, a monopersulfate, a dipersulfate, peracetic acid, apercarbonate, and an organic peroxide. The total weight of the at leastone oxidizing agent having at least one peroxy group may be at least 15percent, at least 25 percent, or at least 35 percent, relative to theweight of the first liquid. For example, the total weight of the atleast one oxidizing agent having at least one peroxy group may be atleast 0.15 grams, at least 0.25 grams, or at least 0.35 grams per gramof the first liquid. This liquid may comprise polar organic solvents,water, acids, and corrosion inhibitors.

[0022] In another embodiment, the first liquid comprises at least onecorrosion inhibitor. The corrosion inhibitor may comprise, for example,at least one of benzotriazole and a derivative of benzotriazole. Thetotal weight of the at least one corrosion inhibitor may be at least 5percent, at least 15 percent, or at least 25 percent, relative to theweight of the first liquid. For example, the total weight of the atleast one corrosion inhibitor may be at least 0.05 grams, at least 0.15grams, or at least 0.25 grams per gram of the first liquid.

[0023] In another embodiment, the method comprises the further steps of(d) introducing a second liquid to a second cluster generation site, thesecond liquid comprising a corrosion inhibitor; (e) subjecting thesecond liquid to electrical forces higher than a surface tension of thesecond liquid to prepare a second plurality of clusters; and (f)impacting clusters of the second plurality clusters upon a secondportion of the surface. The corrosion inhibitor preferably comprisesbenzotriazole or a derivative of benzotriazole. The corrosion inhibitormay alternatively comprise a dihydroxybenzene or trihydroxybenzenecompound. The first and second cluster generation sites may be the same.Such second liquid can be used to apply a blanket or a small amount ofcorrosion inhibitor on the surface.

[0024] The step of (c) impacting may comprise impacting the surface withclusters having a first average kinetic energy and the step of (f)impacting comprises impacting the surface with clusters having a second,smaller average kinetic energy. For example, the step of (f) impactingmay comprise impacting the surface with clusters having an averagekinetic energy at least 15 percent less, at least 25 percent less, or atleast 35 percent less, than an average kinetic energy of the firstplurality of clusters.

[0025] In a preferred embodiment, the cluster generation site comprisesan opening through which liquid is introduced to the cluster generationsite. The liquid exiting the opening and the surface to be impacted withclusters may be subjected to an electrical potential differencetherebetween. During the step of (f) impacting, the absolute potentialdifference may be at least 15 percent less, at least 25 percent less, orat least 35 percent less, than during the step of (c) impacting.

[0026] At least a portion of the second portion of the surface may besubjected to the steps of (f) impacting and (c) impacting. The step of(f) impacting may be performed after initiating the step of (c)impacting.

[0027] In one embodiment, at least a portion of the first portion of thesurface is not subjected to the step of (f) impacting.

[0028] For at least a portion of the second portion of the surface alsosubjected to the step of (c) impacting, the step of (f) impacting may beperformed for a total time T. For at least a time 0.8×T, the step of (f)impacting may be performed without also performing the step of (c)impacting. For example, for a particular portion of the surface, thestep of (c) impacting may be initiated at a time to and carried out for30 seconds. For the same portion of the surface, the step of (f)impacting may be carried out for 100 seconds. Preferably, the step of(f) impacting is performed for at least 80 seconds without concurrentlyperforming the step of (c) impacting. The step of (f) impacting may beperformed after initiating the step of (c) impacting. The step of (f)impacting may be performed after completing the step of (c) impacting.

[0029] In one embodiment, the steps of (c) impacting and (f) impactingare performed while subjecting the first and second portions of thesurface to a gas pressure of less than 500 torr. Preferably, once one ofthe steps of (c) impacting and (f) impacting has been initiated, thefirst and second portions of the surface are not subjected to a gaspressure of greater than 500 torr until at least after the other of thesteps of (c) impacting and (f) impacting has also been initiated.

[0030] At least one of the first and second liquids may be essentiallyfree of metals.

[0031] In one embodiment, the method comprises the steps of: (g)depositing at least one organometallic compound upon a second portion ofthe surface; and (h) annealing the at least one organometallic compoundto thereby provide the second portion of the surface with a metalliccoating. The step of (g) depositing may comprise: (i) introducing athird liquid to a third cluster generation site, the third liquidcomprising the at least one organometallic compound; j) subjecting thethird liquid to electrical forces higher than a surface tension of thethird liquid to prepare a third plurality of clusters; and (k) impactingclusters of the third plurality clusters upon a third portion of thesurface. The first and third cluster generation sites may be the same.

[0032] The step of (g) depositing may comprise depositing at least twodifferent metals upon the second portion of the surface. The metalliccoating may be annealed to provide at least one alloy.

[0033] The steps of (c) impacting and (k) impacting may be performedwhile subjecting the first and third portions of the surface to a gaspressure of less than 500 torr. Preferably, once one of the steps of (c)impacting and (k) impacting has been initiated, the first and secondportions of the surface are not subjected to a gas pressure of greaterthan 500 torr until at least after the other of the steps of (c)impacting and (k) impacting has also been initiated.

[0034] In one embodiment, for at least 1×10⁻⁵ cm² of the third portionof the surface, the step of (g) depositing comprises depositing at leastabout 9×10⁻⁸ g/cm³ of metal, for example, at least about 100×10⁻⁸ g/cm³of metal per square centimeter.

[0035] Another aspect of the invention relates to a method for modifyinga surface. In one embodiment, the method comprises (a) introducing afirst liquid to a first cluster generation site, the first liquidcomprising a reducing agent; (b) subjecting the first liquid toelectrical forces higher than a surface tension of said liquid toprepare a first plurality of clusters; and (c) impacting clusters of thefirst plurality of clusters upon a first portion of the surface.

[0036] The reducing agent may comprise at least one of hydrazine and aderivative of hydrazine. In one embodiment, the total weight of the atleast one of hydrazine and a derivative of hydrazine is at least 5percent, at least 10 percent, or at least 20 percent relative to theweight of the first liquid. For example, the total weight of the atleast one of hydrazine and a derivative of hydrazine may be at least0.05 grams, at least 0.10 grams, or at least 0.20 grams per gram of thefirst liquid.

[0037] Another aspect of the invention relates to a method for modifyinga surface. In one embodiment, the method comprises (a) introducing afirst liquid to a first cluster generation site, the first liquidcomprising an organometallic compound; (b) subjecting the first liquidto electrical forces higher than a surface tension of the first liquidto prepare a first plurality of clusters; and (c) impacting clusters ofthe first plurality of clusters upon the surface, wherein at least someof the organometallic compound deposits upon the surface.

[0038] The method may further comprise (d) subjecting the surfacedeposited organometallic compound to annealing whereby an at leastpartial metallic coating is formed upon the surface. The step ofannealing may comprise heating the surface. The step of annealing maycomprise exposing the surface to at least one gas, for example, ammonia,nitrogen, oxygen, a halogen, and an inert gas, e.g., at least one ofhelium and argon.

[0039] At least two different metals may be deposited upon the surface,wherein subjecting the surface to annealing comprises formation of ametallic alloy upon the surface.

[0040] During the step of impacting the surface with clusters preparedfrom a liquid comprising an organometallic, at least a portion of thesurface may be subjected to an electrical charge whereby the clustersimpacting upon the surface are either attracted to or repelled from thecharged portion of the surface. For example, a conductive portion of thesurface, such as a metallic portion, may be subjected to a charge havingan opposite polarity with respect to a charge upon the clusters wherebyclusters are attracted to the charged portion of the surface andpreferentially impact thereupon as compared to other portions of thesurface. In this embodiment, the average kinetic energy of the clustersmay be less than 500 MeV, for example less than 200 MeV, for exampleless than 50 MeV.

[0041] In one embodiment, a plurality of clusters having a negativecharge are prepared. Electrons are injected into the plurality ofclusters, whereby the clusters acquire an additional negative chargebefore impacting upon the surface. The additional negative charge causesdisruption of the clusters whereby the size of the clusters is furtherreduced.

[0042] Formation of clusters, such as beams of high energy clusters,preferably comprises introducing a liquid to a cluster generation site,which may comprise an opening of a passage, such as an opening of acapillary. The opening by which liquid is introduced to the clustergeneration site may have any suitable shape, such as round, ellipticalor slit-like. More than one opening may be provided.

[0043] By applying an electric field to the cluster generation site, forexample to the tip of a capillary or to the edges of a slit, the fluid,which is preferably conductive, is electrostatically atomized providinga plurality of clusters, which are preferably charged upon formation.The electrical field for atomization, which may be of the order 105volts/cm or greater, may be established by applying a potentialdifference between, for example, the opening of the capillary and acounterelectrode or extractor.

[0044] The charged clusters are electrostatically accelerated by theextraction field to hypervelocities and directed toward a targetsubstrate (e.g., wafer). Because the clusters may be multiply chargedupon formation, acceleration through 10 kV or more results in impactenergies greater than 0.5 million electron volts. Because of theirmassive size compared to the ions of ion beams, clusters expend theirenergy over an extended area of the target causing simultaneous liftoffand removal of particulates having micron and submicron dimensions,organic films and metallic contaminants. Although individual clusterimpact energies are high, the energy is shared by the large number ofcluster nucleons. This results in specific energies at impact less than1 eV/nucleon, well below material sputtering thresholds, preventingdirect etching or damage to impacted surfaces during the contaminantremoval process. Dislodged contaminants may be collected by, forexample, using a cryogenic shroud thereby preventing theirre-introduction on cleansed surfaces. Substrate charging may beprevented by introducing electrons into the plurality of clusters, whichelectrons neutralize the charge on the clusters.

[0045] To increase the area of the target cleansed and decrease the timerequired to remove contaminant species, a plurality of capillaryemitters may be configured into two or more arrays preferably disposedadjacent and parallel to each other. To prevent target substratecharging, charged clusters emitted from single capillary emitters ormultiple arrays are neutralized by ejecting electrons into the beam. Anovel means for cluster beam neutralization uses two arrays; one arrayoperated with positive high voltage to generate positive clusters andthe other operated at negative high voltage to form negative clusters.The array voltages are adjusted independently until the net chargebuildup on a target substrate is approximately zero.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present invention is discussed below in reference to thedrawings in which:

[0047]FIG. 1 is a diagram showing the basic concept and apparatus forproducing charged clusters used to clean or remove contaminants fromsurfaces such as semiconductor wafers in accordance with the presentinvention.

[0048]FIG. 2 shows a capillary emitter for generating a charged clusterbeam subsequently neutralized by injecting electrons into the beam.

[0049]FIG. 3 is a partial perspective view showing a plurality or arrayof capillary emitters in combination with a thermionic electron emittingfilament for beam neutralization.

[0050]FIG. 4 is a perspective view showing a bipolar arrangementconsisting of alternating arrays of positive and negative capillaryemitters for beam neutralization.

[0051]FIG. 5 is a perspective view showing a linear slit capillaryemitter geometry for generating a charged cluster beam.

[0052]FIG. 6 is a perspective view of a capillary cluster emitter withassociated ion optics for focusing and electrostatic deflection forpositioning the cluster beam at designated target areas.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0053] One aspect of the present invention relates to an apparatus andmethod for modifying a surface, such as to remove surface contaminantsand/or to deposit compounds upon the surface. The surface may include,for example, a semiconductor or data storage medium, for example, amagnetically or optically readable storage medium, e.g., a computer harddrive. The surface may comprise a surface have microfabricated surfacefeatures, such as a chemical analysis device having surface featureswith dimensions of less than about 10 microns.

[0054] Methods of the invention preferably comprise subjecting a liquidto electrical forces sufficient to prepare a plurality of clusters ormicrodroplets, which terms are used interchangeably herein. The clusterscomprise material present in the liquid when subjected to the electricalforces. For example, the clusters may comprise solvent and, if present,solutes present in the liquid. As discussed further below, the clusterspreferably have an average diameter smaller than 10 microns, forexample, less than 0.5 micron, such as less than 0.1 micron. Theclusters may have average diameters of at least 0.001 microns, forexample at least 0.005 micron.

[0055] The electrical forces preferably exceed a surface tension of theliquid by an amount sufficient to disrupt droplets of the liquid wherebyclusters are formed. The clusters may also be subjected to electricalforces that accelerate the clusters toward a surface to be impacted withthe clusters. The electrical forces that prepare the clusters may be thesame electrical forces that accelerate the clusters. The electricalforces may be electrostatic or time varying.

[0056] Referring to FIGS. 1 and 2, a device for modifying a surfacecomprises an emitter 32 configured to form a plurality 34 of micron orsubmicron sized clusters. By way of a non-limiting example, the emitter32 can have the form of a capillary having a bore 31 with a diameter of0.0025 to 0.01 cm. An emitter tip 33 seen in FIG. 2, according to aparticularly preferred geometry, tapers at an angle between 20-45°.Although this emitter tip is preferred, satisfactory operation can beobtained with emitters having different end configurations, such as ablunt end. It is fully contemplated within the scope and spirit of theinvention that other emitter geometries are possible that will provideclusters having suitable characteristics. The actual dimensions of thecapillary bore 31 will depend on the desired flow rate and physicalproperties of a fluid 21 introduced to the emitter.

[0057] In a preferred embodiment, the outside diameter 39 of the emittermay be, for example, from 0.02 to 0.0.8 cm, although larger or smallerdimensions may be suitable. The emitter may be formed from manymaterials including materials which are electrically conductive orinsulating. Conductive materials include but are not limited tostainless steel and platinum. Platinum is the preferred material sinceit exhibits excellent resistance to electrochemical corrosion therebyincreasing the lifetime of the emitter 33. Electrically insulatingmaterials include but are not limited to polymers, glass, ceramics andfused silica.

[0058] In a preferred embodiment of the present invention, a fluid 21,which is preferably conductive, such as a conductive liquid, flows froma reservoir 18 through a fluid conduit 20 to the emitter 32. A two-wayshutoff valve (V4) 15 may be inserted in the fluid conduit between thereservoir and capillary emitter as a means of terminating or restartingthe flow of fluid to the emitter. Preferred fluid flow rates for asingle capillary tube emitter 32 are from 0.1 to 3 microliters/minutealthough flow rates outside this range may be used. Fluid flow rates maybe determined by any combination of the geometric flow impedance of theemitter 32; by the pressure above the fluid in the reservoir 18; and bythe fluid temperature.

[0059] The liquid introduced to the emitter may have a temperature ofless than a boiling point of the liquid. In one embodiment, the liquidintroduced to the emitter has a temperature of less than about 200620C., of less than about 150620 C., of less than about 100620 C., or ofless than about 75° C.

[0060] The pressure above the fluid in the reservoir may be regulated bya pressure/vacuum controller 16 which automatically opens and closes acombination of on-off solenoid valves (V1,V2,V3) 14. With valve (V2)closed, opening valve V(1) connects a regulated gas supply 12 and a gasconduit 13 to the reservoir 18 when valve (V3) is open, exposing thefluid to a positive pressure applied by gas supply 12. When valve (V1)is closed, opening valve (V2) connects a vacuum pump 10 to the reservoir18 when valve (V3) is open, reducing the pressure over the fluid inreservoir 18. In this manner, reservoir pressures can be adjusted, butnot limited to, a preferred range of 50 torr to 1500 torr forcontrolling flow rates to the emitter. An inert gas such as helium orargon is preferred for pressurizing the reservoir 18 containing thefluid 21. In general it is recommended that the pressurizing gas usedresist solvation by the fluid thereby reducing the risk of bubbleformation in the fluid conduit 20. The fluid 21 may be degassed beforeloading in the reservoir 18 to reduced to reduce the concentration ofdissolved gasses.

[0061] Flow rates can also be controlled by heating the fluid 21,particularly for fluids whose viscosities show large variations withchanges in temperature. An example of a fluid exhibiting this propertyis one consisting of high concentrations of glycerol or otherpoly-alcohol. Although various conventional means for heating thesolution are available, a satisfactory method is illustrated in FIG. 1.The fluid conduit 20 is vacuum sealed and passes through a vacuum flange24. The vacuum flange in turn is mounted and sealed to a high vacuumchamber 27. A heater 26, preferably a flexible, silicone rubber heaterencloses and is attached to the flange 24. Heat conducted through theflange 24 warms the fluid conduit 20 in intimate contact with theflange. A thermocouple 22 senses the flange temperature which isregulated by a temperature controller 24. Suitable flange temperaturesfor controlling the flow rates of glycerol fluids range from ambient to60° C.

[0062] A preferred liquid used for cluster formation in the presentinvention comprises a solvent, preferably high purity solvent, and,optionally a solute. It should be understood, however, that a solvent isnot required. Preferred solvents have gas phase dipole moments of atleast 1.5 debye, for example, at least 1.70 debye, or at least 1.85debye. The solvent may have a dielectric constant of at least 40, forexample, at least 70, such as at least 80. Examples of preferredsolvents include water and organic solvents including alcohols,poly-alcohols, amines, formamides, ketones, aldehydes, nitriles, andsulfoxides.

[0063] Preferred alcohols have fewer than 30 carbon atoms, such as fewerthan 10 carbon atoms. Examples of preferred alcohols include methanol,ethanol, propanol, and butanol. The solvent may comprise a poly-alcoholpreferably comprising fewer than 30 carbon atoms, for example fewer than20 or fewer than 10 carbon atoms. The poly-alcohol preferably comprisesmore than 2, for example more than 5, or more than 10 hydroxyl groups.Examples of suitable poly-alcohols include ethylene glycol, glycerol,polyethylene glycols, polypropylene glycol and others.

[0064] Preferred formamides include formamide, methyl formamide,dimethyl formamide, and others. Preferred ketones and aldehydes havefewer than 20 carbon atoms, such as fewer than 10 carbon atoms.Exemplary ketones include acetone and methyl ethyl ketone. Exemplarysulfoxides include dimethyl sulfoxide and diethyl sulfoxide.

[0065] The liquid used for cluster formation may comprise a conductivityenhancing compound that enhances the conductivity of the liquid. Theconductivity enhancing compound may comprise a preferably volatile salt.For example, an ammonium halide, preferably a quatemium ammonium halidesuch as an ammonium acetate salt may be used to impart conductivity tothe liquid. Other suitable salts include non-volatile alkali metal saltssuch as NaI, CsI and KI. Preferably, the concentration of salt in theliquid is about 0.1 normal to 2.0 normal.

[0066] In one embodiment of the present invention a surface is impactedwith clusterscomprising at least one oxidizing agent, which may assistin the chemical removal of targeted material on the substrate surface.Preferably, the amount of oxidizing agent used to prepare the clustersis sufficient to assist the removal process, while being as low aspossible to minimize handling, environmental, or similar or relatedissues, such as cost.

[0067] Clusters comprising an oxidizing agent may be prepared by, forexample, a process comprising introducing a liquid comprising one ormore oxidizing agents to a cluster generation site. The liquid may besubjected to electrostatic forces sufficient to prepare clusters fromthe liquid. In one embodiment, the liquid comprises at least 2.5%oxidizing agent, for example, at least 5%, at least 15%, and, in highconcentration embodiments, at least 25%, or event at least 35% oxidizingagent. The liquid may comprise 100% or less oxidizing agent, for exampleless than 75%, or even less than 50% oxidizing agent. In one embodiment,the liquid consists essentially of the at least one oxidizing agent andone or more solvents, for example, water, alcohol, or poly-alcohol.

[0068] Alternatively, the liquid may comprise other compounds inaccordance with the invention including organometallic compounds,corrosion inhibitors and the like.

[0069] An hydroxlamine compound is an exemplary oxidizing agent for usein producing clusters of the present invention. In one embodiment thefluid introduced to the cluster preparation site consists essentially ofat least one hydroxylamine compound. In this embodiment, the clusterspreferably consist essentially of the at least one hydroxylaminecompound. In another embodiment, the fluid introduced to the clusterpreparation site comprises at least one hydroxylamine compound and atleast one other compound. The at least one other compound may comprise,for example, at least one of (a) one or more solvents and (b) at leastone salt. For example, a preferred liquid consists essentially of atleast one hydroxylamine compound and at least one solvent.

[0070] The hydroxylamine compound may comprise, for example, at leastone of hydroxylamine, a salt of hydryoxylamine, a derivative ofhydroxylamine, and a salt of a derivative of hydroxylamine. Thehydroxylamine compound may be organic or inorganic. Preferably, thehydroxylamine compound satisfies the general formula:

[0071] wherein R₃ is hydrogen or a linear, branched, or cyclichydrocarbon containing from 1 to 7 carbon atoms; and wherein X and Yare, independently, hydrogen or a linear, branched, or cyclichydrocarbon containing from 1 to 7 carbon atoms, or wherein X and Y arelinked together form a nitrogen-containing heterocyclic C₄-C₇ ring.

[0072] Examples of preferred hydroxylamine compounds according to theinvention include hydroxylamine, N-methyl-hydroxylamine,N,N-dimethyl-hydroxylamine, N-ethyl-hydroxylamine,N,N-diethyl-hydroxylamine, methoxylamine, ethoxylamine,N-methyl-methoxylamine, and the like.

[0073] It should be understood that hydroxylamine and its derivatives,as defined above, are available (and may be included in a compositionaccording to the invention) as salts, e.g., sulfate salts, nitratesalts, phosphate salts, or the like, or a combination thereof, and theinvention includes these forms of hydroxylamine compounds and theirderivatives. In another embodiment, the composition containshydroxylamine, a sulfate or nitrate salt of hydroxylamine, or acombination thereof. In some embodiments, the liquid introduced to thecluster generation site is substantially free from hydroxylamine and/orderivatives thereof.

[0074] In one embodiment, the composition according to the inventioncomprises an amine compound that is not a hydroxyl-containing amine andis not an alkanolamine. Examples of such amine compounds include, butare in no way limited to, o-diaminobenzene, p-diaminobenzene,N-(2-aminoethyl)-ethylenediamine (“AEEDA”), 2-aminoethyl-ethyleneamine,piperazine, N-substituted piperazine derivatives, piperidine,N-substituted piperidine derivatives, diethylene triamine,2-methyleneaminopropylenediamine, hexaamthylene tetramine, and the like,or a combination thereof.

[0075] Preferably the only oxidizing agent in the first liquidcomposition is an hydroxylamine compound. However, other oxidizingagents can be added or used alternatively.

[0076] The oxidizing agent may comprise an inorganic or organicper-compound. A per-compound is generally defined as a compoundcontaining an element in its highest state of oxidation, such asperchloric acid; or a compound containing at least one peroxy group(—O—O—), such as peracetic acid and perchromic acid. Suitableper-compounds containing at least one peroxy group include, but are notlimited to, urea hydrogen peroxide, a monopersulfate, a dipersulfate,peracetic acid, a percarbonate, and an organic peroxide, such as benzoylperoxide or di-t-butyl peroxide. For example, ozone is a suitableoxidizing agent either alone or in combination with one or more othersuitable oxidizing agents.

[0077] One preferred per compound is periodic acid.

[0078] In a preferred per-compound embodiment, the compound containingat least one peroxy group comprises hydrogen peroxide. For example, theliquid introduced to the cluster generation site may consist essentiallyof hydrogen peroxide or other compound containing at least one peroxygroup. Alternatively, the liquid introduced to the cluster generationsite comprises a solution of a solvent, such as water, hydrogen peroxideor other compound containing at least one peroxy group. The solution mayfurther include a conductivity enhancing compound. The liquid mayconsist essentially of the aforementioned solution with or without theconductivity enhancing compound.

[0079] Suitable per-compounds that do not contain a peroxy groupinclude, but are not limited to, periodic acid, any periodiate salt,perchloric acid, any perchlorate salt, perbromic acid, and anyperbromate salt, perboric acid, and any perborate salt.

[0080] Exemplary oxidizing agents include peroxymonosulfuric acid,potassium peroxymonosulfate, and ammonium peroxymonosulfate.

[0081] Other oxidizing agents are also suitable components of thecomposition of the present invention. Iodates are useful oxidizers.Oxone is a useful oxidizer.

[0082] The oxidizing agent may be a salt of a metal having multipleoxidation states, a complex or coordination compound of a metal havingmultiple oxidation states, or any combination thereof, provided thecompound has a sufficient oxidative potential to oxidize the substrate.hi general, the metal-containing oxidizers are less preferred. Examplesinclude permanganate or salts thereof and perchromate or salts thereof,iron salts, aluminum salts, cerium salts, and the like. When admixedwith another common oxidizer such as hydrogen peroxide in a solution,the salts and oxidizer react and the oxidizing capacity of the mixturemay decline with time. The nature of the reaction is not known, althoughit is known that if the pH is above about 5, iron precipitates asFe(OH)₃ and catalytically decomposes the hydrogen peroxide to oxygen.

[0083] One disadvantage with metal-containing oxidizer salts is thatthey can leave metal contamination on the substrate. This metalliccontamination can result in shorts and spurious conductive properties,along with other problems. Certain metals, such as those with a tendencyto plate on or be absorbed on to at least one part of the substrate, maybe more damaging than other metals. In one embodiment, the total weightof the metal present in the liquid used to make the clusters is lessthan 1 percent, less than 0.5 percent, less than 0.2 percent, less than0.05 percent, less than 0.02 percent or less than 0.005 percent relativeto the weight of the liquid. Clusters of the invention may beessentially free of metals, for example, completely free of metals. Byessentially free of metals it is meant that the total weight of metalpresent in the liquid used to generate the clusters is less than 0.25percent relative to the weight of the liquid. An exception to thispreference are embodiments in which the clusters comprise one or moreorganometallic compounds, which embodiments are discussed elsewhereherein.

[0084] In one embodiment of the present invention, the liquid introducedto the cluster generation site comprises a reducing agent. Hydrazineand/or a derivative of hydrazine are preferred reducing agents. Forexample, the liquid may comprise an aqueous hydrazine solution. Thesolution may comprise at least 10% hydrazine, for example, at least 25%hydrazine. The solution preferably includes at least 90% water, forexample, at least 65% water. Of course, other hydrazine compatiblesolvents may be used in place of or in addition to water.

[0085] In another embodiment of the present invention, the liquidintroduced to the cluster generation site comprises at least onecorrosion inhibitor. Examples of corrosion inhibitors include, but arenot limited to, nitrate salts of ammonium; hydrocarbon-substitutedammonium nitrate salts; catechol; benzotriazole; 2,4-pentandionedioxime; 1,6-dioxaspiro[4,4] nonane 2,7-dione (di-ether); thiourea;ammonium bisulfite; choline bisulfite; choline hydroxide; bischolinehydroxide; trischoline hydroxide; glycerol; sorbitol; gelatine; starch;phosphoric acid; silicic acid; polyethylene oxide; polyethylene imine;and the like; or a combination thereof. Other corrosion inhibitorsinclude choline hydroxide, bischoline hydroxide, or trischolinehydroxide. Preferably, the corrosion inhibitors are substantially freeof metals and/or metal ions. Preferred corrosion inhibitors have boilingpoints in excess of 150° C., in excess of 200° C., or in excess of 250°C.

[0086] In one embodiment, the liquid introduced to the clustergeneration site comprises at least one metal, preferably at least oneorganometallic compound. The liquid may comprise at least one solventand/or at least one other compound in accordance with the presentinvention. In one embodiment, the liquid introduced to the clustergeneration site consists essentially of at least one organometalliccompound and at least one solvent.

[0087] The at least one organometallic compound is preferably a compoundcomprising at least one metal linked or otherwise associated withcarbon. For example, as used herein, the term organometallic compoundincludes compounds having a bonding interaction (ionic or covalent,localized or delocalized) between one or more carbon atoms of an organicgroup or molecule and a metal of a main group, transition, lanthanide,or actinide. The metal may be in the form of, for example, an atom orion. Organic derivatives of the metalloids (e.g. boron, silicon,germanium, arsenic, and tellurium) are considered to be organometalliccompounds. Compounds such as molecular metal hydrides, metal alkoxides,thiolates, amides, phosphides, metal complexes containing organo-group15 and 16 ligands, and metal nitrosyls are also considered to beorganometallic compounds.

[0088] With the aid of FIG. 2, the process of generating a beam ofclusters will now be described. The fluid from reservoir 18 flowsthrough the fluid conduit 20 and is delivered to the emitter 32, whichis preferably exposed to high vacuum. When the fluid reaches thecapillary tip 33, it enters an intense electrostatic field region 37formed by applying high voltage to the emitter 32. A cluster generationsite preferably includes a liquid introduction device, such as theopening of a capillary, by which liquid may be introduced into a regionhaving a pressure of less than about 750 torr, such as less than about100 torr, such as less than about 10-3 torr. The emitter 32 exposed tohigh vacuum and allowing fluid to be introduced to electrostatic fieldregion 37 is an example of a cluster generation site.

[0089] The preferred voltage is in the range +8 to +20 kV and may beapplied using a power supply 17. The electric field 37 is establishedbetween the capillary tip 33 and an extractor electrode 30 whosepotential is adjustable by means of a power supply 19. The relativelyintense fields generated at the capillary tip 33 (>10⁵ volts/cm) resultin electrostatic forces stressing the exposed surface of the fluid. Asthe voltage applied to the emitter 32 is increased, the electrostaticforce acting on the fluid surface at the tip 33 also increases until avalue is reached that exceeds the surface tension force S holding thefluid together. The fluid disrupts into an aggregate of preferablycharged clusters forming a beam of clusters 34 comprising a plurality ofclusters. If a positive high voltage is applied to the emitter 32 bymeans of power supply 17, clusters in a beam 34 will be positivelycharged. Alternatively, if a negative high voltage is applied to theemitter, the beam 34 will consist of negatively charged clusters.

[0090] Clusters with smaller or larger average diameters can begenerated by varying the magnitude of the electric field 37. In general,small clusters, having high charge-to-mass ratios, are generated by highelectric fields while large clusters, having lower charge-to-massratios, are formed at relatively lower electric fields. When a fixedvoltage is applied to the emitter 32, the electric field 37 willincrease or decrease depending on the voltage applied to the extractionelectrode 30. Conversely, by applying a fixed voltage to the extractorelectrode 30, the electric field 37 will increase or decrease dependingon the voltage applied to the emitter 32.

[0091] The energy with which clusters impact a target substrate 38 isdetermined by the voltage applied to the emitter 32, independent of thevoltage applied to the extractor electrode 30. In the preferredembodiment of the invention, it is desirous to keep the voltage appliedto the emitter constant, corresponding to impact energies greater than0.5 MeV, and vary the extractor electrode voltage to generate clusterswith sizes that efficiently remove contaminants. In summary, the voltageapplied to the capillary emitter can be used to control the clusterimpact energy and the voltage applied to the extractor electrode can beused to control the mean cluster size.

[0092] It should be pointed out that the cluster size distribution inthe beam 34 can be modified by other means when the electric field 37 isfixed by the voltages applied to the emitter 32 and the extractorelectrode 30. Mean cluster sizes in the distribution can also be shiftedto yield smaller or larger mean cluster diameters by varying the flowrate of the conductive fluid, with low flow rates corresponding tosmaller clusters and high flow rates corresponding to larger clusters.Finally, for a given fluid flow rate and voltage applied to the emitter32 and extractor electrode 30, the mean cluster size characterizing thedistribution can be modified by varying the conductivity of the fluid21. For the purpose of removing micron and submicron particulates fromwafer surfaces, clusters with mean diameters in the range 0.01-0.05micron are preferred. From the foregoing discussion, it is apparent thatthe system provides sufficient flexibility to adjust the processvariables for producing clusters with desired sizes and energies toefficiently remove particulate or organic film contaminants fromsurfaces.

[0093] The cluster beam 34, formed by electrostatically dispersing thefluid at the capillary tip 33, is accelerated by the electric field 37existing in the gap separating the emitter 32 from the extractorelectrode 30. In a preferred embodiment of the invention, a circularopening or extractor aperture 35 in the extractor electrode 30 has adiameter whose dimensions are on the order of 0.3 to 0.95 cm. Forsymmetry considerations, the extractor aperture 35 is usually circular,if the emitter 32 is tubular, but it is possible to use other shapes.The preferred alignment of the emitter-extractor electrode combinationconsists of placing the emitter 32 coaxially at the center of theextractor aperture 35 such that the capillary tip 33 lies in themid-plane of the extractor electrode 30. Although this arrangement ispreferred, satisfactory operation can be achieved if the capillary tip33 is positioned directly behind the rear surface of the extractorelectrode 30 to a distance of 0.3 cm. Further retraction of the emitter32 can cause excessive impingement of the cluster beam 34 on thebackside of the extractor electrode 30. Bombardment of the extractorelectrode 30 by charged clusters in the beam eject secondary electronsthat are accelerated back to the capillary tip 33 causing uncontrolledtip heating when a positive high voltage is applied to the emitter 32.

[0094] As seen in FIG. 1, the cluster beam 34 formation and accelerationprocess is preferably carried out in a vacuum chamber 27. A stationaryor transportable target substrate 38 is interposed in the cluster beam34. In a preferred embodiment of the invention, a non-focused, divergentcluster beam impacts the target substrate 38. In this manner, a largearea of the substrate can be impacted as opposed to a smaller areaimpacted by a focused beam. Individual clusters in the beam impact thesurface of the target substrate 38 resulting in the effective removal ofvarious types of contaminants. In some instances and for efficaciousremoval of contaminants, it is desirable to rotate the target substrate38 with respect to the cluster beam 34 allowing impacts to occur atacute angles of incidence. Contaminants driven from the target substrate38 may deposit on the surfaces of a cryogenic collector 36, cooled byliquid nitrogen or other means preventing their re-deposition on thecleansed substrate surface. An alternate impaction or collection surfacemay consist of an uncoated, porous, sintered metal mesh or a teflonmembrane filter. Particulates removed from surfaces by the impact ofcluster beams provide an extremely light loading on collection surfaces.In view of the loading conditions, an oil-coated teflon membrane filtercan provide a surface with a collection efficiency of 100% as discussedby C. Tsai, “Solid Particle Collection Characteristics on ImpactionSurfaces of Different Designs”, Aerosol Sci.Technol., 23, 96,1995. Anoil for applying a thin coating to collection surfaces is preferably onehaving an extremely low vapor pressure about 10⁻¹⁰ torr) e.g., asilicone diffusion pump fluid, Model D-7050, manufactured by DowCorning. Metal or dielectric surfaces charged by application of voltagescan suffice for collecting ejected particulate contaminants in someapplications.

[0095] Several properties of the cluster impacts are important andrelevant to the processes of contaminant removal and deposition. Clustervelocities may be supersonic and, depending on the acceleration voltageapplied to the emitter 32, can exceed the velocity of sound in theimpacted material. It is believed that shock waves can be induced in thematerial impacted (substrate 38, films or particulates) causing shockunloading or liftoff of contaminant species. Because individual clusterscan carry a large number of charges (N>100), clusters acceleratedthrough 10 kV or more have impact energies of the order 0.5 to 2.0 MeV'swhich are deposited over an extended area of the target substrate 38.The direct transfer of a portion of this collisional energy can overcomeLondon—Van der Waals and electrostatic forces bonding contaminants tosurfaces.

[0096] The massiveness of individual clusters in the beam 34, preferablyon the order of 10-17 to 10-16 grams, in combination with theirsupersonic velocities, provides a means for transferring a largemomentum to film and particulate contaminants, especially for eventsinvolving multiple and energetically additive collisions.

[0097] A unique feature of the present invention is that, compared toatomic ion or small molecular ion beams, the massiveness of the clustersemployed here for cleaning contaminated surfaces insures that the totalcluster energy is shared by the large number of nucleons comprising theclusters. Although the total cluster energy may exceed 1 MeV, individualnucleons which participate in collisions have specific energies lessthan 1 eV/nucleon. On the atomic level, damage or sputtering of thetarget substrate is prevented. In the preferred embodiment of theinvention, this is a critical feature since contaminants must be removedwithout causing substrate damage or removal of permanent featuresessential for operating devices constructed from the substrate material.Another unique feature of the present invention is that beam clustersare comparable in size to individual particulate contaminants withdiameters less than 1 micron. Submicron clusters are particularlyeffective for interacting with and removing particulates less than 0.1micron, a particularly troublesome size if future microelectronicsdevices are to provide features with sizes approaching 0.07 micron.

[0098] In some embodiments of the present invention it is desired todeposit at least some material present in the clusters upon the impactedsurface. For example, as discussed above, clusters comprising one ormore corrosion inhibitors may be impacted upon a surface. In anotherembodiment, clusters comprising one or more metals, such as one or moreorganometallic compounds are impacted upon a surface. When depositingmaterial upon a surface it is preferred to reduce the average kineticenergy of the clusters with respect to the average kinetic energy ofclusters used to remove contaminants. For example, in preferredembodiments clusters having energies of less than about 1.5 MeV, forexample, less than 0.75 MeV, less than 0.5 MeV, or even less than 0.4MeV may be used to deposit material upon a surface.

[0099] In one embodiment, of the present invention the surface issubjected to impact with clusters prepared from a first liquid. Thesurface is also subjected to impact with clusters prepared from a secondliquid, which may be different from the first liquid. For example, thesecond liquid may include a different solvent and/or solute from thefirst liquid. In a preferred embodiment, clusters prepared from thefirst liquid remove particulates or other contaminants from the surface.It is preferred that material present in clusters prepared from thefirst liquid essentially does not deposit upon the surface. Materialpresent in clusters prepared from the second liquid, however, may bedesirably deposited upon at least a portion of the surface. Suchdeposited material may include at least one of corrosion inhibitors andcompounds comprising a metal.

[0100] In deposition mode, clusters having a lower kinetic energy may beprepared by reducing the absolute electrical potential of the emitter ascompared to the absolute electrical potential of the emitter whenclusters are prepared to remove contaminants. The potential of theemitter may be determined relative to the potential of the surface of beimpacted. In one embodiment, for example, a first plurality of clustersis impacted upon a surface to remove contaminants therefrom. A secondplurality of clusters may then be impacted upon at least a portion ofthe surface to deposit at least some material present in clusters of thesecond plurality of clusters upon the surface. Clusters of the secondplurality of clusters may have kinetic energies at least 10% less, atleast 25% less, or at least 50% less than clusters of the firstplurality of clusters.

[0101] In a preferred embodiment, the step of impacting the surface withclusters prepared from the second liquid occurs after the step ofimpacting with surface with clusters prepared from the first liquid hasbeen initiated. A given area of the surface may first be subjected toimpact with clusters prepared from the first liquid and then subjectedto impact with clusters prepared from the second liquid. If the step ofimpacting with clusters prepared from the second liquid is performedsubsequent to the step of impacting with clusters prepared from thefirst liquid, it is preferred that the surface not be exposed toenvironments comprising excessive number of particulates in betweenperforming the two steps. For example, the surface is preferably notexposed to environments comprising more than 1000 particulates of adiameter exceeding 0.5 microns per square foot of atmosphere in betweenthe two steps. More preferably, the surface is preferably not exposed toenvironments comprising more than 100 particulates of a diameterexceeding 0.5 microns per square foot of atmosphere in between the twosteps. The term particulates, as used in this context, does not includeclusters prepared in accordance with the present invention.

[0102] During the steps of impacting with the first and second liquids,the surface is preferably exposed to a pressure of less than 500 torr,for example less than 100 torr or even less than 10 torr. If the step ofimpacting with clusters prepared from the second liquid is performedsubsequent to the step of impacting with clusters prepared from thefirst liquid, it is preferred that the surface not be exposed to apressure of greater than 500 torr, 100 torr, or 10 torr in betweenperforming the two steps.

[0103] If means are not provided for bleeding off excess charge buildupon the target substrate 38, surface charging can occur in the presenceof the cluster beam 34. The buildup of potential by surface charging canlead to beam deceleration, reducing the impact energy of the clusters.Further, variations in the potentials between neighboring regions on thetarget substrate 38 can promote local discharging causing damage tosubstrate features. In the present embodiment of the invention, aneutralization method is employed to prevent charging of the substrateexposed to a positively charged cluster beam. Referring to FIG. 2, athermionic emitter 44, preferably made from tantalum or other refractorymaterial which emits copious electrons on being heated, is positionedbelow the extractor electrode 30. The thermionic emitter 44 ispreferably constructed from small diameter wire, in the range 0.010 to0.020 inches, and bent in a circle symmetrically positioned on thelongitudinal axis of the tubular capillary emitter 32. The thermionicemitter 44 can be heated by means of a filament power supply 46 andbiased a few volts negative by means of a power supply 48 which providesthe energy necessary to launch the electrons along trajectories 42.Electrons escaping the thermionic emitter 44 leave by way of a circularopening placed in the neutralizer shield 40. Neutralization of thecluster beam can be accomplished by trapping electrons within the beamand by the capture of electrons by individual, positively chargedclusters. Alternative means for injecting electrons into a beam forneutralization exist with different configurations and materials andneed not be discussed here without departing from the scope or spirit ofthe present invention.

[0104] In order to provide multiple cluster beams for impacting andcleaning larger surface areas and for decreasing the time required toremove contaminants, a second embodiment of the processing apparatuswill now be described. FIG. 3 illustrates a linear array consisting of aplurality of emitters 32 for generating multiple, cluster beams. When aplurality of emitters form an array that is linear, hexagonally packedor configured to some other suitable geometry, a single extractorelectrode 30 having multiple, circular apertures 35 may be used. Themultiaperture extractor electrode provides the geometry required toestablish the intense electric fields at each of the capillary emitterscomprising the array. Neutralization of the multiple beams can beprovided by a single thermionic emitter 44 described previously for usewith a single capillary emitter, configured to conform to the lineardimensions of the array. Positive high voltage in the range +8 to +20kV, preferably +15 kV in the present embodiment, is applied to each ofthe capillary emitters by means of a power supply 17. The individualemitters comprising the array can be wired in parallel as shown in FIG.3.

[0105] As an alternate to using a plurality of emitters 32, a linearcapillary slit 62 as shown in FIG. 5 may be provided. By applyingvoltage to the capillary slit, a plurality of emissive sites will beformed in the fluid along the slit edges, resulting in the production ofplural beams of clusters. The preferred width of the slit channel 64filled with fluid 21 is of the order 0.001 to 0.004 inches. In FIG. 5 aslotted extractor electrode 60 aids in establishing the intense electricfield at the slit edges. Beam neutralization for this configuration (notshown) can be provided by an electron emitting wire filament as seen inFIG. 3.

[0106] With the aid of FIG. 4, a novel means for providing beamneutralization is accomplished by employing two or more linear arrays.The left side of FIG. 4 illustrates a linear array consisting of aplurality of capillary emitters 32 wired in parallel to a power supply17. Positively charged cluster beams will be generated by the array whenpositive high voltage is applied by means of power supply 17. Similarly,the right side of FIG. 4 illustrates an adjacent linear array consistingof a plurality of capillary emitters 32 wired in parallel to powersupply 23. Negatively charged cluster beams will be formed by the arraywhen negative voltage is applied by means of a power supply 23. Usingthis bipolar arrangement, beams consisting of positively and negativelycharged clusters can be generated simultaneously. Beam neutralizationcan be achieved by adjusting the positive and negative voltages appliedby power supplies 17 and 23 until the net charge buildup on the targetsubstrate 38 is approximately zero.

[0107] An alternate embodiment of the invention allows for an ionoptical system capable of focusing and deflecting the cluster beam. Bypositioning the beam at precise locations on a target substrate,contaminants can be removed from a first portion of the surface withsubjecting a second portion of the surface to impaction with clusters.FIG. 6 shows a three-element electrostatic lens 50 used to focus thecluster beam 34 generated by an emitter 32. In this arrangement, afocusing voltage is applied to the mid-element lens plate by means of apower supply 52. The polarity of the applied voltage will depend onwhether a positive or negative cluster beam is formed. Although FIG. 6shows a symmetrical, Einzel aperture type lens, other types andgeometries of electrostatic lenses can be used to control cluster beamswithout departing from the scope or spirit of the present invention.These include slit, tubular cylinders and geometrically asymmetriclenses. Electrostatic deflection and rastering to precisely position thecluster beam on the substrate 38 can be provided by a set of orthogonaldeflector plates 56, 58—controlled by applying variable or fixedvoltages by means of a rastering power supply 54.

[0108] A focused or deflected cluster beam may be used to depositmaterial upon only selected portions of a surface leaving little or nomaterial deposited upon other portions of the surface. For example, inone embodiment of the invention, a first portion of a surface issubjected to impact with clusters of a first plurality of clusters toremove contaminants from the surface or otherwise prepare the surfacefor deposition of a material, for example, a corrosion inhibitor ormetal. A second portion of the surface is impacted with clusters of afocused second plurality clusters, the clusters comprising a material tobe deposited upon the second portion of the surface. The second portionof the surface preferably comprises a subset of the first portion of thesurface. For example, the second portion of the surface may comprise anetwork of one or more electrical connections.

[0109] The foregoing description of the preferred embodiment of theinvention has been presented for the purposes of illustration anddescription. However, the foregoing description is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manychanges and modifications may be made to the invention by one havingordinary skill in the art, without departing from the spirit or scope ofthe invention.

What is claimed is:
 1. A method of modifying a work-piece surface, themethod comprising: (a) introducing a first liquid to a first clustergeneration site, the first liquid comprising hydroxylamine orhydroxylamine derivative compound; (b) subjecting the first liquid toelectrical forces higher than a surface tension of the first liquidunder conditions to prepare a first plurality of clusters; and (c)impacting at least a portion of the clusters of the first plurality ofclusters upon a first portion of the surface.
 2. The method of claim 1,wherein the oxidizing agent comprises at least one of aqueoushydroxylamine or a hydroxylamine substituted with one or two R groupswhich can independently be a C₁ to C₄ alkyl and a carboxyl,or saltthereof.
 3. The method of claim 2, wherein the first liquid furthercomprises a solvent.
 4. The method of claim 2, wherein, relative to theweight of the first liquid, the total weight of the at least one ofhydroxylamine, the derivative of hydroxylamine, the salt ofhydroxylamine, and the a salt of a derivative of hydroxylamine is atleast 15 percent.
 5. The method of claim 4, wherein the oxidizing agentcomprises at least one of hydroxylamine and a derivative ofhydroxylamine and the total weight thereof is at least 15 percentrelative to the weight of the liquid.
 6. The method of claim 3, whereinthe first liquid consists essentially of the solvent and the at leastone of hydroxylamine, the derivative of hydroxylamine, the salt ofhydroxylamine, and the a salt of a derivative of hydroxylamine.
 7. Themethod of claim 3, wherein the solvent comprises an organic compoundhaving at least one hydroxyl group.
 8. The method of claim 7, whereinthe solvent comprises an organic compound having fewer than 20 carbonatoms and at least two hydroxyl groups.
 9. The method of claim 1,wherein the first liquid comprises an acid.
 10. The method of claim 9,wherein the acid comprises at least one of nitric acid, acetic acid,sulfuric acid, peroxymonosulfuric acid, perchloric acid, peracetic acid,perchromic acid, periodic acid, perchloric acid, perbromic acid,perfluoric acid, and perboric acid.
 11. The method of claim 1, whereinthe first liquid comprises at least one corrosion inhibitor.
 12. Themethod of claim 11, wherein the corrosion inhibitor comprises at leastone of benzotriazole and a derivative of benzotriazole.
 13. A method ofmodifying a work-piece surface, the method comprising: (a) introducing afirst liquid to a first cluster generation site, the first liquidcomprising periodic acid or hydrogen peroxide; (b) subjecting the firstliquid to electrical forces higher than a surface tension of the firstliquid under conditions to prepare a first plurality of clusters; and(c) impacting at least a portion of the clusters of the first pluralityof clusters upon a first portion of the surface.
 14. The method of claim13, wherein the total weight of the at least one oxidizer having atleast one peroxy group is at least 15 percent relative to the weight ofthe first liquid.
 15. The method of claim 13, wherein the first liquidcomprises at least one corrosion inhibitor.
 16. The method of claim 13,wherein the corrosion inhibitor comprises at least one of benzotriazoleand a derivative of benzotriazole.
 17. The method of claim 1, furthercomprising: (d) introducing a second liquid to a second clustergeneration site, the second liquid comprising a corrosion inhibitor; (e)subjecting the second liquid to electrical forces higher than a surfacetension of the second liquid to prepare a second plurality of clusters;and (f) impacting clusters of the second plurality clusters upon asecond portion of the surface.
 18. The method of claim 17, wherein thestep of (c) impacting comprises impacting the surface with clustershaving a first average kinetic energy and the step of (f) impactingcomprises impacting the surface with clusters having a second, smalleraverage kinetic energy.
 19. The method of claim 18, wherein the step of(f) impacting comprises impacting the surface with clusters having anaverage kinetic energy at least 25% less than an average kinetic energyof the first plurality of clusters.
 20. The method of claim 17, whereinthe corrosion inhibitor comprises at least one of benzotriazole and aderivative of benzotriazole.
 21. The method of claim 17, wherein thecorrosion inhibitor comprises at least one of a dihydroxybenzene ortrihydroxybenzene.
 22. The method of claim 17, wherein at least aportion of the second portion of the surface is also subjected to thestep of (c) impacting.
 23. The method of claim 22, wherein the step of(f) impacting is performed after initiating the step of (c) impacting.24. The method of claim 22 wherein, for the portion of the secondportion of the surface also subjected to the step of (c) impacting, thestep of (f) impacting is performed for a total time T, and furtherwherein the step of (f) impacting is performed for at least a time 0.8×Tsubsequent to terminating the step of (c) impacting.
 25. The method ofclaim 17, wherein the steps of (c) impacting and (f) impacting areperformed while subjecting the first and second portions of the surfaceto a gas pressure of less than 500 torr and, once one of the steps of(c) impacting and (f) impacting has been initiated, the first and secondportions of the surface are not subjected to a gas pressure of greaterthan 500 torr until at least after the other of the steps of (c)impacting and (f) impacting has also been initiated.
 26. The method ofclaim 17, wherein at least a portion of the first portion of the surfaceis not subjected to the step of (f) impacting.
 27. The method of claim17, wherein the first and second cluster generation sites are the same.28. The method of claim 1, wherein the first liquid is essentially freeof metals.
 29. The method of claim 1, further comprising the steps of:(g) depositing at least one organometallic compound upon a secondportion of the surface; and (h) annealing the at least oneorganometallic compound to thereby provide the second portion of thesurface with a metallic coating.
 30. The method of claim 29, wherein thestep of (g) depositing comprises: (i) introducing a third liquid to athird cluster generation site, the third liquid comprising the at leastone organometallic compound; (j) subjecting the third liquid toelectrical forces higher than a surface tension of the third liquid toprepare a third plurality of clusters; and (k) impacting clusters of thethird plurality clusters upon a third portion of the surface.
 31. Themethod of claim 29, wherein the step of (g) depositing comprisesdepositing at least two different metals upon the second portion of thesurface, and wherein the metallic coating provided in the step of (h)annealing comprises at least one alloy.
 32. The method of claim 22,wherein the steps of (c) impacting and (k) impacting are performed whilesubjecting the first and third portions of the surface to a gas pressureof less than 500 torr and, once one of the steps of (c) impacting and(k) impacting has been initiated, the first and second portions of thesurface are not subjected to a gas pressure of greater than 500 torruntil at least after the other of the steps of (c) impacting and (k)impacting has also been initiated.
 33. The method of claim 29, whereinthe step of (c) impacting comprises impacting the surface with clustershaving a first average kinetic energy and the step of (k) impactingcomprises impacting the surface with clusters having a second, smalleraverage kinetic energy.
 34. The method of claim 32, wherein the step of(k) impacting comprises impacting the surface with clusters having anaverage kinetic energy at least 25% less than an average kinetic energyof the first plurality of clusters.
 35. The method of claim 29, whereinat least a portion of the first portion of the surface is also subjectedto the step of (k) impacting.
 36. The method of claim 35, wherein thestep of (k) impacting comprises focusing clusters of the third pluralityof clusters.
 37. The method of claim 31, wherein, for at least 1×10⁻⁵cm² of the third portion of the surface, the step of (g) depositingcomprises depositing at least about 9×10⁻⁸ g/cm³ of metal per squarecentimeter.
 38. The method of claim 29, wherein the first and thirdcluster generation sites are the same.
 39. A method for modifying asurface, the method comprising: (a) introducing a first liquid to afirst cluster generation site, the first liquid comprising a reducingagent; (b) subjecting the first liquid to electrical forces higher thana surface tension of said liquid to prepare a first plurality ofclusters; and (c) impacting clusters of the first plurality of clustersupon a first portion of the surface.
 40. The method of claim 39, whereinthe reducing agent comprises at least one of hydrazine and a derivativeof hydrazine.
 41. The method of claim 40, wherein the total weight ofthe at least one of hydrazine and a derivative of hydrazine is at least10 percent relative to the weight of the first liquid.
 42. The method ofclaim 40, wherein the first liquid is essentially free of metals. 43.The method of claim 40, further comprising: (d) introducing a secondliquid to a second cluster generation site, the second liquid comprisinga corrosion inhibitor; (e) subjecting the second liquid to electricalforces higher than a surface tension of the second liquid to prepare asecond plurality of clusters; and (f) impacting clusters of the secondplurality clusters upon the surface.
 44. The method of claim 43, whereinthe corrosion inhibitor comprises at least one of benzotriazole and aderivative of benzotriazole.
 45. A method for modifying a surface, themethod comprising: (a) introducing a first liquid to a first clustergeneration site, the first liquid comprising an organometallic compound;(b) subjecting the first liquid to electrical forces higher than asurface tension of the first liquid to prepare a first plurality ofclusters; and (c) impacting clusters of the first plurality of clustersupon the surface, wherein at least some of the organometallic compounddeposits upon the surface.
 46. The method of claim 45, furthercomprising the step of: (d) subjecting the surface depositedorganometallic compound to annealing whereby an at least partialmetallic coating is formed upon the surface, wherein the step of (c)impacting comprises depositing at least two different metals upon thesurface and the step of (d) subjecting comprises formation of a metallicalloy upon the surface.